This invention relates to a process and an apparatus for testing commercial vehicle parts such as axles and/or springs and/or one or more other components adjacent thereto. The parts are subjected by means of at least one vertical force generator to vertical forces of the type occurring when a commercial vehicle is in use while the spring of the commercial vehicle is fixed by means of a supporting assembly at that one or more points of attachment corresponding to the point or points at which it is attached to the body of the commercial vehicle.
The spring suspension of commercial vehicles has the function of compensating for irregularities on the ground and absorbing the forces transmitted from the roadway. Furthermore, the axle is guided by means of leaf springs so that all the forces transmitted from the wheel into the axle are introduced into the frame by way of the springs. A reliable test for strength in test stands taking into account all types of loads under loading conditions simulating those occurring in practice is therefore of the utmost importance.
The loads to which commercial vehicle springs are subjected will first be described with reference to FIGS. 1 and 2:
The loads on commercial vehicle springs are produced by the following forces resulting from irregularities on the ground and driving maneuvers: EQU Vertical forces F.sub.V EQU Lateral forces .+-.F.sub.S EQU Longitudinal forces .+-.F.sub.L EQU Braking and driving forces .+-.F.sub.B
These forces acting on the front axle spring 3 through the front axle 1 and the rear axle spring 4 through the rear axle 2 of the commercial vehicle 5 are entered in FIGS. 1 and 2 and have the following causes and significanes:
(a) Vertical forces F.sub.V : The vertical forces F.sub.V result from the static preload due to the weight of the vehicle itself, quasi-static weight displacements on cornering, with compression of one of the two vehicle springs while the other is under expansion, quasi-static weight displacements with symmetric spring compression on braking, dynamic forces occurring simultaneously on both sides on travelling over elevations in the ground, transverse grooves, rails or the like, and accidental loads when driving over irregularities in the ground. The latter are relatively high frequency loads which occur on both sides of the vehicle independently of one another.
(b) Lateral forces .+-.F.sub.S : Quasi-static lateral forces act during cornering, positive lateral forces +F.sub.S acting from the wheels on the outside of the curve towards the center of the vehicle while negative lateral forces -F.sub.S act from the wheels on the inside of the curve towards the outside of the vehicle. High frequency dynamic lateral forces occur when the vehicle travels over irregularities on the ground and potholes; in such cases, the direction of action on each wheel may extend alternately in both directions so that both positive and negative lateral forces .+-.F.sub.S occur.
(c) Longitudinal forces .+-.F.sub.L : High frequency longitudinal forces .+-.F.sub.L act at the center of the axle stub both in the rearward direction as positive longitudinal forces +F.sub.L and in the forward direction as negative longitudinal forces -F.sub.L. They constitute the horizontal component of any impact transmitted obliquely into the rotating wheel such as occurs when the vehicle travels over irregularities in the ground.
(d) Braking and driving forces .+-.F.sub.B : Braking forces +F.sub.B and driving forces -F.sub.B act on the contact surface of the wheel tread as a result of a driving maneuver and in accordance with the maneuver carried out.
Vertical forces, lateral forces, longitudinal forces and driving and braking forces may also occur as a reaction to asymmetric deformation of the frame, asymmetric spring excursions and cornering.
The overall deformations of springs of commercial vehicles listed below result from the co-operation of the forces described above:
(1) Symmetric and asymmetric spring excursions due to vertical forces F.sub.V acting on the wheel.
(2) Twisting about the longitudinal axis due spring excursions (moment about the longitudinal axis).
(3) Lateral displacement due to lateral forces .+-.F.sub.S and possibly also twisting.
(4) S-deformation due to braking and driving forces +F.sub.B
(5) Longitudinal stress produced by longitudinal forces .+-.F.sub.L in combination with spring excursions or S-impact.
(6) Twisting about the vertical axis due to differential braking or longitudinal forces.
To explain the state of the art of testing commercial vehicle springs and the difficulties inherent in the testing technique hitherto available, reference will now be made to FIGS. 1 to 4 and the documents cited below which show several test stands for carrying out such tests and illustrate schematically the difference between the testing technique hitherto available and the actual conditions prevailing when commercial spring vehicles are under load on the road:
(1) Betriebslastensimulation an Fabrzeugbauteilen mittels servohydraulischer Pruufeinrichtungen (Operational Load Simulation on Vehicle Parts by means of Servohydraulic Test Devices), G. Jacoby, SCHENCK in: VDI-Berichte No. 632, 1987, FIG. 18.
(2) Simulation von Betriebsbeansprunchungen fur den Lebensdauernachweis von Leichtbaublattfedern (Simulation of Operational Stresses for Testing the Service Life of Lightweight Leaf Springs), H. Oppermann and D. Schutz FhG-Berichte 2/3, 1987, pages 23-29.
(3) Prufung im Automobilbau, (Testing in the Manufacturing of Automobiles), G. Jacoby, from the Lecture entitled "Prufung von Werkstoffen und Maschinenbauteilen mittels programmierbarer elektrohydraulischer Prufmaschinen"; (Testing of Materials and Machine Parts by means of Programmed Electrohydraulic Test Machines), Prague, 28-30.11.1984, CARL SCHENCK AG.
Reference will first be made to a test stand in which the hitherto most widely practiced testing technique is carried out. In this test stand, a leaf spring of a commercial vehicle is fixed to the test stand by its two longitudinal ends at which it is normally connected to the car body when it is in the assembled vehicle while a vertical force generator acts as the only force generator of the test stand on that point at which the axle is normally connected in the assembled commercial vehicle. This hitherto most widely used testing technique thus takes into account only the simulation of vertical spring excursions. It is not possible by these means to obtain any reliable information on the service life of the commercial vehicle spring since the other loads occurring in practice are not accounted for.
The test stand illustrated in FIG. 18 of Document 1 for simultaneously testing two leaf springs which are rigidly connected together at the points at which they are normally connected to the axle comprises two vertical force generators, a lateral force generator and a braking force generator. Such a test stand may therefore be used to simulate lateral forces and braking forces in addition to vertical forces but it is less suitable for simulating the complex forces to which leaf springs are subjected to load conditions on the road, the reasons for this being as follows:
(a) Since the leaf springs are fixed at their longitudinal ends in the test stand, the forces acting on them are not a true reflection of the conditions prevailing in practice. This falsification will now be explained with reference to FIGS. 3 and 4, FIG. 3 indicating schematically the conditions occurring in practice under driving conditions while FIG. 4 shows the conditions in the test stand of FIG. 18 of Document 1. Since the longitudinal ends of the leaf spring are in practice fixed to the body 6 of the vehicle while the longitudinal centers of the springs are fixed to the axle 7, testing of the leaf springs in the test stand shown in FIG. 18 of Document 1 amounts to a reversal of the conditions occurring in practice since the car body 6 in the test stand remains parallel to the horizontal, which corresponds to the roadway, as shown in FIG. 4, whereas under practical driving conditions, for example when the vehicle is cornering, the car body 6 together with the frame is inclined to the horizontal or the roadway, as shown in FIG. 3, and the axle 7 remains virtually parallel to the roadway, apart from any inclination due to compression of the tires.
Considerable falsifications occur in the test stand shown in FIG. 18 of Document 1 due to the force generators acting on the axle substitute construction. This manner of introducing loads and the oblique positioning of the axle substitute construction, which corresponds to oblique positioning of the whole axle 7 of FIG. 4 in relation to the roadway, causes the directions of action of the vertical forces F.sub.V, the L lateral forces .+-.F.sub.S and the braking forces .+-.F.sub.B to be falsified to such an extent that large errors and coupling faults may occur. In contrast to the situation occurring in practice, in which the axle remains virtually parallel to the roadway and the vertical forces are introduced at right angles to the axle and the lateral forces parallel to the axle (see FIG. 3), the situation found in the test stand of FIG. 18 of Document 1 is that, in contrast to the conditions occurring in practice, the vertical forces are introduced in a direction which is not perpendicular to the vehicle axle and the lateral forces are introduced in a direction which is not parallel to the axle, as may be seen from FIG. 4.
(b) Since all the force generators in the test stand shown in FIG. 18 of Document 1 act on the axle substitute construction, the vertical forces, lateral forces and braking forces cannot be introduced independently of one another and therefore influence one another, all the more so when the axle is set obliquely, as discussed with reference t FIG. 4.
(c) Since the test stand shown in FIG. 18 of Document 1 is equipped with only one lateral force generator and one braking force generator, it cannot simulate the lateral forces and braking forces which in practice act independently of one another on both sides of the axle of the vehicle.
(d) The vertical forces produce large spring excursions, so that high test frequencies which would correspond to frequencies occurring in practice cannot be achieved.
There still remains to be mentioned the test stand described in Document 2, which is designed for testing the strength of individual leaf springs and not for testing the whole assembly comprising wheel, axle and springs.
In test installations for testing vehicle axles subjected to multi-axial introduction of forces, the axle is either fitted into the complete vehicle or mounted in a test frame. The principles on which this is carried out are illustrated for passenger vehicles in Document 1, FIGS. 23 to 26, and for trucks and lorries in Document 3, FIGS. 63 to 67.
Common to all these test installations is that the wheel forces act against the mass of the vehicle, which may be either locked in position or free to move but which, in contrast to conditions occurring on the road, remains largely in position while the roadway must be inclied. In this case, as also in the spring test stand illustrated in Document 2, the force generators must simulate the entire spring excursions, with the result that both the frequency of testing which can be attained and the quality of simulation when testing the complete axles are impaired. It is therefore necessary to compensate for the influence of the force components on one another by means of an elaborate electronic correction of the geometry.
It is an object of the present invention in particular to provide a process and an apparatus for testing commercial vehicle axles and springs whereby the components of the axle can be tested under loading conditions similar to those occurring in practice, thereby eliminating the above mentioned, in some cases serious disadvantages of known test apparatus.
The process according to the invention for testing the axles or springs of commercial vehicles, in which the commercial vehicle axle or spring is subjected to vertical forces of the type occurring when a commercial vehicle is in use while the axle or spring is held by a supporting assembly at the point or points of attachment by which said axle or spring is normally attached to the body of the commercial vehicle, is distinguished according to the invention in that for testing the axle and/or spring of a commercial vehicle and/or one or more other, adjacent components under loading conditions similar to those occurring in practice, the supporting assembly is mounted to be moveable and the axle and/or spring and/or other component(s) of the commercial vehicle is or are subjected by way of the moveable supporting assembly to at least those vertical forces which correspond to a static and/or low frequency loading of the commercial vehicle axle and/or spring and/or other component(s) while those parts of the commercial vehicle axle through which wheel forces are introduced in the vertical direction of action are kept substantially fixed in position or only moved with vertical forces of a magnitude which correspond to a relatively high frequency loading of the axle and/or spring and/or other component(s) of the commercial vehicle. The vertical forces corresponding to a static and/or low frequency loading of the commercial vehicle axle or spring are those vertical forces which bring about the main excursions of compression and expansion of the commercial vehicle springs, which are followed by the movement of the supporting assembly.
This arrangement always enables the vertical forces to be introduced in the same manner as occurs under driving conditions regardless of the degree to which the springs of the vehicle are compressed so that the corresponding falsifications discussed above are avoided. The resulting spring excursions are small and in particular a vertical force preload may be produced on which a low frequency and/or relatively high frequency vertical force load may be superimposed. These and other advantages are described in more detail below.
As a further development of the invention, there is provided a process in which, instead of or in addition to being subjected to vertical forces, the axle and/or spring and/or other component(s) of the commercial vehicle is or are subjected to lateral forces and/or longitudinal forces and/or braking or driving forces of the kind occurring when a commercial vehicle is in use. These forces are introduced either through those points of attachment of the vehicle spring which correspond to its attachment to the axle of the vehicle and/or through the axle of the vehicle itself. This further development is distinguished according to the invention in that for testing the spring of the commercial vehicle and/or the axle connected thereto and/or the other component(s) under load conditions resembling those occurring in practice, the lateral forces and/or longitudinal forces and/or braking or driving forces are introduced into the axle and/or spring and/or other component(s) of the commercial vehicle by way of the commercial vehicle axle connected to the spring or by way of at least one wheel or wheel substitute connected to the commercial vehicle axle and optionally by way of a brake force transmitting lever.
A further feature of the process according to the invention is distinguished in that for testing the axle of the commercial vehicle and/or two commercial vehicle springs and/or the other component(s) under loading conditions resembling those occurring in practice, at least two commercial vehicle springs are held by the supporting assembly, preferably in the manner in which they are fixed to the body of a commercial vehicle when in use, most preferably by means of original parts connected to the commercial vehicle axle which is provided on each side with wheels or wheel substitutes, optionally in each case in combination with a brake force transmitting lever.
Under these conditions, the axle of the commercial vehicle can be held fixed in the direction of spring compression and expansion apart from vertical displacements which are small compared with the maximum excursion of compression and expansion of the commercial vehicle spring(s), in particular less than 10%, preferably less than 5% of the mentioned maximum excursion of the spring. This corresponds to real operating conditions to a high degree.
The supporting assembly may be mounted to pivot about a pivot shaft which is capable of parallel displacement in the direction of spring excursion and which preferably extends in a direction perpendicular to the direction of spring excursion and perpendicular to the axial direction of the vehicle axle.
When the process is carried out with two commercial vehicle springs, the pivot shaft may be guided to undergo parallel displacement along a straight line which is equidistant at every point to the two commercial vehicle springs.
Further, the pivot shaft is preferably held in the plane in which the vehicle spring is fixed, in particular in the plane of the spring bushes or brackes, plus or minus the height of the commercial vehicle springs, when the supporting assembly is in the load free or statically loaded state.
Particularly short spring excursions of compression and expansion are obtained when the vertical forces act in the line of action or close to the line of action of the commercial vehicle spring or springs.
Furthermore, when the process is carried out with two commercial vehicle springs, the vertical forces may be arranged to act on the supporting assembly in such a manner that when they act simultaneously, they give rise to symmetric compression of both commercial vehicle springs, and when they act alternately, they give rise to compression of one spring with simultaneous expansion of the other spring. For testing two commercial vehicle springs alone, the lateral force and the braking or driving force may be introduced between the ends of the commercial vehicle axle, in particular centrally between the two ends of the axle, in each case by way of a force transmitting means extending from the point of introduction of the force to the wheel or wheel substitute or the brake force transmitting lever of the one or other end of the axle, and longitudinal forces need only be introduced at one point. Lastly, relatively high frequency vertical forces may be introduced into the axle and/or spring(s) and/or other component(s) of the commercial vehicle by way of the vehicle axle, in particular by way of at least one wheel or a wheel substitute connected to the axle or a brake force transmitting lever attached thereto.
The apparatus for testing commercial vehicle axles and/or springs provided by the invention is distinguished according to the invention in that for testing the axle and/or spring and/or other component(s) of the commercial vehicle under loading conditions resembling those occurring in practice, the supporting assembly is mounted to be moveable and the moveable assembly is coupled to at least one vertical force generator for producing at least vertical forces of the kind corresponding to a static and/or low frequency loading of the commercial vehicle axle and/or spring while that point of attachment of the commercial vehicle spring which corresponds to its point of attachment to the axle of the commercial vehicle and/or that point on the commercial vehicle axle through which the wheel forces are introduced is/are held in a substantially fixed position in the direction of action of the vertical force generator or are moveable by means of a further vertical force generator which, however, produces only those vertical forces which correspond to a relatively high frequency loading of the commercial vehicle axle and/or spring(s) and/or other component(s).
This apparatus is preferably so designed that the supporting assembly is mounted to pivot about a preferably horizontal pivot shaft. Further, the pivot shaft is guided for parallel displacement by means of at least one, preferably vertical guide. In particular, the pivot shaft may be guided by one guide on each side of the supporting assembly.
It is particularly advantageous to arrange the pivot shaft so that when the supporting assembly is coupled to at least state, the shaft lies in the plane containing the means for fixing the commercial vehicle springs, in particular the spring bushes or brackets, plus or minus the height of the load free commercial vehicle springs.
According to a particularly preferred embodiment of the invention, the supporting assembly is coupled to at least two vertical force generators arranged so that the points of their connection to the supporting assembly are arranged symmetrically with respect to the pivot shaft. The vertical force generator or generators may be coupled to the supporting assembly in such a manner that the connecting points lie in the line of action of the spring or springs of the commercial vehicle.
Further developments of the invention are stated in the subclaims to which specific reference is made here as disclosure of further features of the invention.